Update: August 2024 Arctic Heatwave

This updates my post from August 8 about the northwest North America heatwave. For completeness I repeat some of the information in that earlier post here.

****August 16, 2024 addition: I’ve added a graphic (Fig. 1a) showing the ERA5-Land 10km resolution maximum hourly temperature (°C) between August 4 and August 10. This does not replace the in situ observations of maximum temperature but does give an improved idea of the extent of the extreme temperatures.****

For the second summer in a row, extreme, all-time record heat has baked parts of northwest Canada and Alaska. In 2023, the July 8-9 heatwave was centered in the middle and upper Mackenzie River valley and central and southern Yukon Territory, with the Alaska-Yukon borderlands and northern Southeast Alaska on the edge (for details see my post here).

How hot was it?

Figure 1 plots the highest reported temperatures August 5-9, 2024. The most extreme heat relative to the climatology occurred north of the Brooks Range and east of the Richardson Mountains. South of the Brooks Range there were a few daily records. Most notably, the high temperature of 87F (30.6C) at Northway (southeast of Tok) on August 6 is the highest temperature so late in the summer.

Alaska North Slope

Temperatures peaked on the central and eastern Alaska Beaufort Sea coast on August 6. Climate observations have been made in the Deadhorse/Prudhoe Bay area since December 1968, and the high temperature of 89F (31.7C) is by far the highest temperature in that time, breaking the previous record of 85F (29.4C) on July 13, 2016. This is also the highest temperature on record in Alaska north of 70°N latitude and is the second the August in a row with extreme heat in this area: on August 5, 2023, Deadhorse reached 84F (28.9C), which was, as it turned out, a short-lived monthly record high temperature.

The lower Mackenzie River valley

The high temperature on August 7 of 34.8C (95F) at Inuvik is easily the highest temperature on record. The previous record was 33.0C (91F) set July 4, 2023. At Tuktoyaktuk, on the shore of the Beaufort Sea, the high temperature August 7 of 29.9C (86F) was not an all-time record (30.4C, 87F in July 1998) but is a new August record high. Fort McPherson has a very broken period of climate observations but the high of 35.1C (95F) on August 8 was higher than last July’s high temperature by 3.0C (5.4F). Paulatuk, 250 miles (400km) north-northeast of Inuvik also set an all-time record high at 31.0C (88F) on August 9.

The middle Mackenzie River valley (Sahtu region)

High temperatures on August 9 at Fort Good Hope (37.0C, 99F) and Norman Wells (36.7C, 98F) were both monthly record highs but fell just short of the records set on July 8, 2023. However, in some ways this is at least as impressive as last summer’s heat, inasmuch as it occurred a month later in the summer, when clear sky solar heating at 66°N is already about 15 percent lower than it is in early July. And speaking of latitude, as far as I know, the 36.3C (97C) at Little Chicago on August 8 and 9 is the highest temperature on record in Canada north of the Arctic Circle.

Fig. 1 Highest temperatures reported August 5-9, 2024. Data from Environment and Climate Change Canada, NWS and FAA. In Alaska, the warmest day was August 5 or 6, in the Yukon Territory August 6 or 7 and in the Northwest Territories August 7 or 8, except August 9 Fort Good Hope southward.

Fig. 1a 10km gridded maximum one-hour temperature between August 4 and 10, 2024. This highlights the large area east of Inuvik and northwest of Norman Wells, NWT that experienced excessively high temperatures. Also note the high temperature in the immediate Mackenzie River delta. Data from ERA5 Land courtesy of ECMWF/Copernicus.

Overnight low temperatures

In some areas overnight temperatures were also exceptionally high. Hillsides around Fairbanks saw temperatures remain above 60F (16C) August 6 and 7. Continuous strong south winds at Delta Junction/Fort Greely (between Fairbanks and Tok) from the evening of August 5 through the early morning of August 8 kept temperatures elevated day and night. The result was the low temperature on August 6 was only 71F (21.7C), which is not only the highest minimum daily temperature on record at Delta Junction/Fort Greely (previous record 70F/21.1C August 4, 1999) but may well be the highest daily minimum temperature anywhere in Alaska.

At Inuvik, the low temperature August 8 was only 19.5C (67F), which is above the average daily high temperature for early August but was not a monthly record.

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Why was it so hot?

The mid-atmosphere pattern supporting this heatwave is shown in Fig. 2a through 2c. This pattern is a classic for supporting summer heat in northwest North America. On August 5, a large warm high pressure aloft was centered over the southern Yukon Territory and strong low pressure anchored over the Bering Sea. Over the next several days the high pressure aloft drifted east while low in the Bering Sea expanded eastward. To the west of the high center, strong south winds from the Gulf of Alaska all the way into the Beaufort Sea served to increase the temperature of the air mass through latent heat release caused by water vapor being precipitated out on the south slopes of the coastal mountains, Alaska Range, Brooks Range/Richardson Mountains and then warming as the air descends on the north side of the mountains.

Fig. 2a August 5, 2024 500 hPa average heights and departures from the 1991-2020 baseline. Data from NCEP/NCAR R1 reanalysis courtesy NOAA/PSL/ESRL.

Fig. 2b August 7, 2024 500 hPa average heights and departures from the 1991-2020 baseline. Data from NCEP/NCAR R1 reanalysis courtesy NOAA/PSL/ESRL.

Fig. 2c August 9, 2024 500 hPa average heights and departures from the 1991-2020 baseline. Data from NCEP/NCAR R1 reanalysis courtesy NOAA/PSL/ESRL.

Impacts from the heat

An immediate impact from the sustained hot and dry weather across the Northwest Territories was the dramatic growth of wildfires: 575k ha (1.4 million acres) burned in the first 11 days of August. The Yukon Territory saw an uptick in wildfire activity on August 7 and 8 but the reported acreage increase was small. In Alaska, most of the wildfires were inactive due to the rainy and cool weather in late July and the first days of August, though smoke was evident from some of the larger fires north of Fairbanks, and the Sinnott Fire near Eagle flared up, but little to no acreage increases were reported.

An obvious question is what impact these level of heat have on things like permafrost and ecosystems that have not evolved in these conditions. Being early August, North Slope permafrost lies below the seasonally thawed active layer, and so this heat will be integrated with the rest of the summer warmth as it works down into the ground. On the other hand, short term extreme heat can increase thaw slumps along river banks and hillsides and coastlines, where permafrost may be already exposed or only slightly protected. For vegetation, temperatures this high result in rapid drying through increased potential evaporation.

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Technical details:

All dates here are in local time (not Greenwich Mean Time)

Ogimet is an excellent online resource for near-real time Canadian (and most other countries) daily climate observations.

High frequency temperature data direct from Environment and Climate Change Canada for the Northwest Territories here and for the Yukon Territory here.

Canadian climate normals and extremes available here, Canadian daily climate observations available here.

Alaska climate data mostly pulled from the xmACIS website.

The NCEP/NCAR reanalysis is available here and remains a useful tool for large scale free atmosphere evaluation.

The Alaska Interagency Coordination Center is the first stop for all things wildfire-related in Alaska, here.

Up-to-date wildfire information for the Yukon Territory, here, and for the Northwest Territories here.